A fluorescent tube lamp 100 is one of the most widely used lighting technologies today, because fluorescent tubes are more energy efficient than incandescent lamps. FIG. 1 shows an example of a typical fluorescent tube lamp assembly. In recent times, lamps utilizing light emitting diodes have been utilized for their lower energy consumption and longer life, thereby replacing incandescent lamps, compact fluorescent lamps and fluorescent tubes.
An LED lamp 110 as a replacement for a fluorescent tube 100 typically includes several tens or hundreds of small LEDs 111 assembled on one or more printed circuit boards 115. The LED circuit board(s) is typically enclosed in a housing including a metallic housing 116 and a transparent plastic housing 117. The metallic portion 116 of the housing acts as a heat dissipater while the plastic portion 117 of the housing protects the LEDs from external environments. FIG. 2 shows an example of an LED light tube assembly.
Since the LED light tube is a replacement of the fluorescent tube, an end cap structure 112 for the LED light tube is compatible with an end cap 102 for the fluorescent tube lamp. In the fluorescent tube lamp and the LED light tube lamp, two bi-pin end caps are typically disposed on each end of the tube (see, FIGS. 1-3). In some applications, instead of bi-pin end cap 102, a single-pin end cap 103 may be utilized (see. FIG. 4).
The fluorescent tube lamp is connected to a power source by being inserted to sockets 104. The fluorescent lamp is operated by allowing electricity to pass through the fluorescent tube via the bi-pins from one end to another end of the tube. The fluorescent tube is operable regardless of the orientation of the tube when the tube is inserted into the sockets of tube holders. Typically, the fluorescent tune lamp is utilized together with a fluorescent tube ballast and a starter.
When the LED light tube is utilized to replace the fluorescent tube in a lighting fixture, the fluorescent tube ballast and starter, if any, are removed from the lighting fixture during installation of the LED light tube. The sockets are then wired directly to AC main power lines including a power line and a neutral line (i.e., a ground line).
As set forth above, the LED light tube typically includes metallic portion 116. The metallic portion of the LED light tube functions to dissipate heat away from the LEDs, a printed circuit board and a LED driver into the air through convection. However, the metallic portion 116, typically made of extruded aluminum, is electrically conductive as well. This may cause an electrical hazard when there is any leakage from an internal circuit or the AC power lines to the metallic portion.
Accordingly, it has been necessary to implement a safety device that protects the user from electrical shock in case of electricity leakage. More particularly, a safety device will be necessary when the LED light tube is being inserted into the sockets of the tube holder of a lighting fixture.
FIGS. 5 and 6 show one example of an end cap having a safety device in a known device. A cross sectional view of the internal mechanism of the conventional end-cap 201 is illustrated in FIG. 6. In this conventional example, an end-cap 201 for the LED light tube incorporates a push button switch assembly 203. This push button switch assembly 203 is activated by a spring 205 connected to switch cap 202, protruding from an end surface of the end-cap housing 204. As the LED tube is inserted into the socket, the switch cap 202 is depressed by a wall of the socket and the switch cap 202 in turn pushes the button switch 206 located underneath the switch cap 202, which are disposed inside the end-cap housing 204. The button switch 206 closes an electrically open circuit by shorting two internal electrical terminals 211, 212 via a bridging contact plate 210 disposed at the end of the push button switch 206.
The push button assembly 203 in the conventional end-cap 201 poses a few problems in practice. One problem is that the push button 203 may sometimes fail to close the circuit and may not electrically connect the terminal 211 and 212 when the end cap 202 is depressed, because of the two springs 205 and 209. More specifically, since the two springs 205 and 209 are connected in series, they may be insufficiently compressed to force the bridging contact plate 210 to be into contact with the electrical terminals 211 and 212. Thus, it has been necessary to design the end-cap 201 such that the spring force and displacement thereof consistently deliver and release the necessary force to “open” and to “close” the circuit whenever the LED light tube is inserted into or taken out of the socket 104. Failure to do so would cause unexpected turning-off of the LED light tubes or might cause electrical shock to the user.
Furthermore, when the switch cap 202 is depressed, there is friction generated between the switch cap 202 and the cap housing 204 and between a push button shank and its housing when the shank slides inside the push button assembly 203. These frictional forces often result in contact failures due to lack of connecting terminals 211 and 212.
Another problem with the conventional end cap switch is that the speed at which the bridging contact plate 210 connects electrically with the terminals 211 and 212 is generally slow, thereby causing “arcing” between the terminals. The arcing likely occurs when an air-gap between the terminals 211 and 212 is small enough for the electrical charges to build up between the bridging contact plate 210 and the terminals 211 and 212. When a sufficient potential exists between the contacts, the electricity jumps across the air-gap.
This arcing will cause the surfaces of the bridging contact plate 210 and the terminals 211 and 212 to erode and to form oxides that reduce electrical conductivity. This may result in an intermittent switch “off” problem. In a more severe situation, the arcing may also cause the terminals 211 and 212 to fuse with the contact plate 210, resulting in a permanent switch “on” position.
Accordingly, there is a need for an end cap switch for the LED tube lamps which overcomes the foregoing problems and which is more reliable and has a longer life.